Piston rods of hydraulic cylinders as well as other movable parts of hydraulic installations, fittings, valves and shafts to operate locks and bridges offshore and aboard of vessels are subjected to a very hostile environment causing corrosion resulting in a substantially reduced lifetime. A protection against corrosion for all these components made of regular steel, i.e. carbon steel is thus a must when they should maintain their ability to be actuated .
As a rule, piston rods and similar parts are coated with a metallic layer of chrome and/or nickel chrome. However, such layers are susceptible against chemical agents resulting in localized corrosion like pitting, wherein the chrome layer is corroded from outside so that the part becomes defective after some time.
The artisan is of course further aware to make mechanical parts of stainless steel which are coated with a chrome layer to be wear resistant. Parts made this way are extremely expensive.
According to some further prior art (German patent 33 37012) a pump plunger is provided with a ceramic coating. However,
the plunger is made of a nickel-chrome alloy which is extremely expensive.
According to some further art (German 28 50 210) spikes made of stainless steel and carrying a ceramic layer are welded to steam boiler tubes for protection. According to a further proposal an aluminum oxide layer including TiO2 is applied to material such as tubing in combustion chambers which material is subjected to high heat stress.